1. Field of the Invention
The present invention relates to systems and methods for determining the volumetric ratio of liquid suspended solids with respect to the suspending liquid. In particular, the present invention relates to systems and methods for measuring "hematocrit", which is the percent ratio of blood cells per unit of whole blood.
2. Description of the Prior Art
Hematocrit is defined as packed blood cell volume, generally expressed as a percent per 100 milliliters of whole blood.
Hematocrit is one of several laboratory determinations with respect to red blood cells in human blood, or the blood of other animals. Two other allied determinations are that of red blood cell count per cubic milliliter and hemoglobin, which is expressed as grams per 100 milliliters. To a hematologist, computations of ratios involving these three determinations are of considerable value.
The first of these ratios is the mean corpuscular volume (MCV) which is determined by multiplying hematocrit by 10 and dividing the result by the red blood cell count expressed in millions per cubic millimeter, such that MCV is expressed in cubic microns. This ratio approximates red blood cell (erythrocyte) size.
The second ratio is the mean corpuscular hemoglobin (MCH) which is determined by multiplying hemoglobin by 10 and dividing the result by blood cell count expressed in millions per cubic millimeters, such that MCH measurements are expressed in micromicrograms. This ratio approximates the hemoglobin per cell by weight.
The third ratio is the mean corpuscular hemoglobin concentration (MCHC), which is determined by multiplying hemoglobin by 100 and dividing the result by the hematocrit. This ratio is expressed in percent, and approximates hemoglobin concentration in red blood cells by volume. Of these three ratios (MCV, MCH, and MCHC), only MCH may be calculated without knowledge of the hematocrit.
Hematocrit has traditionally been determined in the laboratory by centrifuging small tubes of blood in order to pack the cells in the bottom of the tubes. Results obtained in this manner, which is referred to as microhematocrit, vary as between centrifuges and operators.
Automated equipment for measuring hematocrit fall into two categories. One such arrangement employs the centrifuging techniques discussed previously, with automatic loading, unloading and interpretation.
The second type of automated hematocrit measuring system involves electronic processing of signals obtained by measuring conductivity in proportion to cell size when a dilute solution of cells is passed between two electrodes. Examples of this type of arrangement are described in U.S. Pat. Nos. 3,692,410 to Jurany et al. and 3,439,267 to Coulter et al.
In addition, other types of automated blood analyzing systems are commercially available which are not capable of determining hematocrit. Many of these systems utilize photometry techniques, whereby a characteristic of the amount of light absorbed by a blood sample is processed to determine red blood cell count and hemoglobin.
Other systems and techniques for analyzing the volumetric or particulate ratio of liquid suspended particles are disclosed in the following U.S. Pat. Nos.: 3,740,143 to Groner et al.; 3,646,352 to Bol et al.; 2,775,159 and 3,045,123 to Frommer. Carr, in U.S. Pat. No. 3,714,444, discloses a reflective light measuring system employing a logarithmic ratio converter for providing a single output representative of the concentration of suspended solids.
With respect to the measurement of MCV, Stevens, in U.S. Pat. No. 3,084,591, discloses a system for measuring this characteristic. Pelavin, in U.S. Pat. No. 3,634,868 teaches an automatic calibration circuit useful in fluid sampling systems.